X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fcmm%2FCmmSpillReload.hs;h=a4bedb0baabc871866f9a84371000153b67db921;hp=2dcfb027a39861679b9e5594872bf061bf29ac86;hb=ffd3bd85a6febeec05c99d0da7dfdf34cad59caf;hpb=ee5addccd1929a7368a39b2c88d1b77f0bc8fb73 diff --git a/compiler/cmm/CmmSpillReload.hs b/compiler/cmm/CmmSpillReload.hs index 2dcfb02..a4bedb0 100644 --- a/compiler/cmm/CmmSpillReload.hs +++ b/compiler/cmm/CmmSpillReload.hs @@ -1,9 +1,8 @@ -{-# LANGUAGE GADTs, NoMonoLocalBinds, FlexibleContexts, ViewPatterns #-} +{-# LANGUAGE GADTs, NoMonoLocalBinds, FlexibleContexts #-} -- Norman likes local bindings -- If this module lives on I'd like to get rid of this flag in due course {-# OPTIONS_GHC -fno-warn-warnings-deprecations #-} -{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-} #if __GLASGOW_HASKELL__ >= 701 -- GHC 7.0.1 improved incomplete pattern warnings with GADTs {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} @@ -15,7 +14,6 @@ module CmmSpillReload --, insertSpillsAndReloads --- XXX todo check live-in at entry against formals , dualLivenessWithInsertion - , rewriteAssignments , removeDeadAssignmentsAndReloads ) where @@ -25,14 +23,11 @@ import Cmm import CmmExpr import CmmLive import OptimizationFuel -import StgCmmUtils import Control.Monad import Outputable hiding (empty) import qualified Outputable as PP import UniqSet -import UniqFM -import Unique import Compiler.Hoopl hiding (Unique) import Data.Maybe @@ -52,8 +47,15 @@ A variable can be expected to be live in a register, live on the stack, or both. This analysis ensures that spills and reloads are inserted as needed to make sure that every live variable needed after a call is available on the stack. Spills are pushed back to -their reaching definitions, but reloads are dropped wherever needed -and will have to be sunk by a later forward transformation. +their reaching definitions, but reloads are dropped immediately after +we return from a call and will have to be sunk by a later forward +transformation. + +Note that we offer no guarantees about the consistency of the value +in memory and the value in the register, except that they are +equal across calls/procpoints. If the variable is changed, this +mapping breaks: but as the original value of the register may still +be useful in a different context, the memory location is not updated. -} data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet } @@ -178,9 +180,6 @@ insertSpillAndReloadRewrites graph procPoints = deepBwdRw3 first middle nothing nothing _ _ = return Nothing -regSlot :: LocalReg -> CmmExpr -regSlot r = CmmStackSlot (RegSlot r) (widthInBytes $ typeWidth $ localRegType r) - spill, reload :: LocalReg -> CmmNode O O spill r = CmmStore (regSlot r) (CmmReg $ CmmLocal r) reload r = CmmAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r) @@ -202,458 +201,6 @@ removeDeadAssignmentsAndReloads procPoints g = nothing _ _ = return Nothing ----------------------------------------------------------------- ---- Usage information - --- We decorate all register assignments with usage information, --- that is, the maximum number of times the register is referenced --- while it is live along all outgoing control paths. There are a few --- subtleties here: --- --- - If a register goes dead, and then becomes live again, the usages --- of the disjoint live range don't count towards the original range. --- --- a = 1; // used once --- b = a; --- a = 2; // used once --- c = a; --- --- - A register may be used multiple times, but these all reside in --- different control paths, such that any given execution only uses --- it once. In that case, the usage count may still be 1. --- --- a = 1; // used once --- if (b) { --- c = a + 3; --- } else { --- c = a + 1; --- } --- --- This policy corresponds to an inlining strategy that does not --- duplicate computation but may increase binary size. --- --- - If we naively implement a usage count, we have a counting to --- infinity problem across joins. Furthermore, knowing that --- something is used 2 or more times in one runtime execution isn't --- particularly useful for optimizations (inlining may be beneficial, --- but there's no way of knowing that without register pressure --- information.) --- --- while (...) { --- // first iteration, b used once --- // second iteration, b used twice --- // third iteration ... --- a = b; --- } --- // b used zero times --- --- There is an orthogonal question, which is that for every runtime --- execution, the register may be used only once, but if we inline it --- in every conditional path, the binary size might increase a lot. --- But tracking this information would be tricky, because it violates --- the finite lattice restriction Hoopl requires for termination; --- we'd thus need to supply an alternate proof, which is probably --- something we should defer until we actually have an optimization --- that would take advantage of this. (This might also interact --- strangely with liveness information.) --- --- a = ...; --- // a is used one time, but in X different paths --- case (b) of --- 1 -> ... a ... --- 2 -> ... a ... --- 3 -> ... a ... --- ... --- --- This analysis is very similar to liveness analysis; we just keep a --- little extra info. (Maybe we should move it to CmmLive, and subsume --- the old liveness analysis.) - -data RegUsage = SingleUse | ManyUse - deriving (Ord, Eq, Show) --- Absence in map = ZeroUse - -{- --- minBound is bottom, maxBound is top, least-upper-bound is max --- ToDo: Put this in Hoopl. Note that this isn't as useful as I --- originally hoped, because you usually want to leave out the bottom --- element when you have things like this put in maps. Maybe f is --- useful on its own as a combining function. -boundedOrdLattice :: (Bounded a, Ord a) => String -> DataflowLattice a -boundedOrdLattice n = DataflowLattice n minBound f - where f _ (OldFact x) (NewFact y) - | x >= y = (NoChange, x) - | otherwise = (SomeChange, y) --} - --- Custom node type we'll rewrite to. CmmAssign nodes to local --- registers are replaced with AssignLocal nodes. -data WithRegUsage n e x where - Plain :: n e x -> WithRegUsage n e x - AssignLocal :: LocalReg -> CmmExpr -> RegUsage -> WithRegUsage n O O - -instance UserOfLocalRegs (n e x) => UserOfLocalRegs (WithRegUsage n e x) where - foldRegsUsed f z (Plain n) = foldRegsUsed f z n - foldRegsUsed f z (AssignLocal _ e _) = foldRegsUsed f z e - -instance DefinerOfLocalRegs (n e x) => DefinerOfLocalRegs (WithRegUsage n e x) where - foldRegsDefd f z (Plain n) = foldRegsDefd f z n - foldRegsDefd f z (AssignLocal r _ _) = foldRegsDefd f z r - -instance NonLocal n => NonLocal (WithRegUsage n) where - entryLabel (Plain n) = entryLabel n - successors (Plain n) = successors n - -liftRegUsage :: Graph n e x -> Graph (WithRegUsage n) e x -liftRegUsage = mapGraph Plain - -eraseRegUsage :: Graph (WithRegUsage CmmNode) e x -> Graph CmmNode e x -eraseRegUsage = mapGraph f - where f :: WithRegUsage CmmNode e x -> CmmNode e x - f (AssignLocal l e _) = CmmAssign (CmmLocal l) e - f (Plain n) = n - -type UsageMap = UniqFM RegUsage - -usageLattice :: DataflowLattice UsageMap -usageLattice = DataflowLattice "usage counts for registers" emptyUFM (joinUFM f) - where f _ (OldFact x) (NewFact y) - | x >= y = (NoChange, x) - | otherwise = (SomeChange, y) - --- We reuse the names 'gen' and 'kill', although we're doing something --- slightly different from the Dragon Book -usageTransfer :: BwdTransfer (WithRegUsage CmmNode) UsageMap -usageTransfer = mkBTransfer3 first middle last - where first _ f = f - middle :: WithRegUsage CmmNode O O -> UsageMap -> UsageMap - middle n f = gen_kill n f - last :: WithRegUsage CmmNode O C -> FactBase UsageMap -> UsageMap - -- Checking for CmmCall/CmmForeignCall is unnecessary, because - -- spills/reloads have already occurred by the time we do this - -- analysis. - -- XXX Deprecated warning is puzzling: what label are we - -- supposed to use? - -- ToDo: With a bit more cleverness here, we can avoid - -- disappointment and heartbreak associated with the inability - -- to inline into CmmCall and CmmForeignCall by - -- over-estimating the usage to be ManyUse. - last n f = gen_kill n (joinOutFacts usageLattice n f) - gen_kill a = gen a . kill a - gen a f = foldRegsUsed increaseUsage f a - kill a f = foldRegsDefd delFromUFM f a - increaseUsage f r = addToUFM_C combine f r SingleUse - where combine _ _ = ManyUse - -usageRewrite :: BwdRewrite FuelUniqSM (WithRegUsage CmmNode) UsageMap -usageRewrite = mkBRewrite3 first middle last - where first _ _ = return Nothing - middle :: Monad m => WithRegUsage CmmNode O O -> UsageMap -> m (Maybe (Graph (WithRegUsage CmmNode) O O)) - middle (Plain (CmmAssign (CmmLocal l) e)) f - = return . Just - $ case lookupUFM f l of - Nothing -> emptyGraph - Just usage -> mkMiddle (AssignLocal l e usage) - middle _ _ = return Nothing - last _ _ = return Nothing - -type CmmGraphWithRegUsage = GenCmmGraph (WithRegUsage CmmNode) -annotateUsage :: CmmGraph -> FuelUniqSM (CmmGraphWithRegUsage) -annotateUsage vanilla_g = - let g = modifyGraph liftRegUsage vanilla_g - in liftM fst $ dataflowPassBwd g [(g_entry g, fact_bot usageLattice)] $ - analRewBwd usageLattice usageTransfer usageRewrite - ----------------------------------------------------------------- ---- Assignment tracking - --- The idea is to maintain a map of local registers do expressions, --- such that the value of that register is the same as the value of that --- expression at any given time. We can then do several things, --- as described by Assignment. - --- Assignment describes the various optimizations that are valid --- at a given point in the program. -data Assignment = --- This assignment can always be inlined. It is cheap or single-use. - AlwaysInline CmmExpr --- This assignment should be sunk down to its first use. (This will --- increase code size if the register is used in multiple control flow --- paths, but won't increase execution time, and the reduction of --- register pressure is worth it.) - | AlwaysSink CmmExpr --- We cannot safely optimize occurrences of this local register. (This --- corresponds to top in the lattice structure.) - | NeverOptimize - --- Extract the expression that is being assigned to -xassign :: Assignment -> Maybe CmmExpr -xassign (AlwaysInline e) = Just e -xassign (AlwaysSink e) = Just e -xassign NeverOptimize = Nothing - --- Extracts the expression, but only if they're the same constructor -xassign2 :: (Assignment, Assignment) -> Maybe (CmmExpr, CmmExpr) -xassign2 (AlwaysInline e, AlwaysInline e') = Just (e, e') -xassign2 (AlwaysSink e, AlwaysSink e') = Just (e, e') -xassign2 _ = Nothing - --- Note: We'd like to make decisions about "not optimizing" as soon as --- possible, because this will make running the transfer function more --- efficient. -type AssignmentMap = UniqFM Assignment - -assignmentLattice :: DataflowLattice AssignmentMap -assignmentLattice = DataflowLattice "assignments for registers" emptyUFM (joinUFM add) - where add _ (OldFact old) (NewFact new) - = case (old, new) of - (NeverOptimize, _) -> (NoChange, NeverOptimize) - (_, NeverOptimize) -> (SomeChange, NeverOptimize) - (xassign2 -> Just (e, e')) - | e == e' -> (NoChange, old) - | otherwise -> (SomeChange, NeverOptimize) - _ -> (SomeChange, NeverOptimize) - --- Deletes sinks from assignment map, because /this/ is the place --- where it will be sunk to. -deleteSinks :: UserOfLocalRegs n => n -> AssignmentMap -> AssignmentMap -deleteSinks n m = foldRegsUsed (adjustUFM f) m n - where f (AlwaysSink _) = NeverOptimize - f old = old - --- Invalidates any expressions that use a register. -invalidateUsersOf :: CmmReg -> AssignmentMap -> AssignmentMap --- foldUFM_Directly :: (Unique -> elt -> a -> a) -> a -> UniqFM elt -> a -invalidateUsersOf reg m = foldUFM_Directly f m m -- [foldUFM performance] - where f u (xassign -> Just e) m | reg `regUsedIn` e = addToUFM_Directly m u NeverOptimize - f _ _ m = m -{- This requires the entire spine of the map to be continually rebuilt, - - which causes crazy memory usage! -invalidateUsersOf reg = mapUFM (invalidateUsers' reg) - where invalidateUsers' reg (xassign -> Just e) | reg `regUsedIn` e = NeverOptimize - invalidateUsers' _ old = old --} - --- Note [foldUFM performance] --- These calls to fold UFM no longer leak memory, but they do cause --- pretty killer amounts of allocation. So they'll be something to --- optimize; we need an algorithmic change to prevent us from having to --- traverse the /entire/ map continually. - -middleAssignment :: WithRegUsage CmmNode O O -> AssignmentMap -> AssignmentMap - --- Algorithm for annotated assignments: --- 1. Delete any sinking assignments that were used by this instruction --- 2. Add the assignment to our list of valid local assignments with --- the correct optimization policy. --- 3. Look for all assignments that reference that register and --- invalidate them. -middleAssignment n@(AssignLocal r e usage) assign - = invalidateUsersOf (CmmLocal r) . add . deleteSinks n $ assign - where add m = addToUFM m r - $ case usage of - SingleUse -> AlwaysInline e - ManyUse -> decide e - decide CmmLit{} = AlwaysInline e - decide CmmReg{} = AlwaysInline e - decide CmmLoad{} = AlwaysSink e - decide CmmStackSlot{} = AlwaysSink e - decide CmmMachOp{} = AlwaysSink e - -- We'll always inline simple operations on the global - -- registers, to reduce register pressure: Sp - 4 or Hp - 8 - -- EZY: Justify this optimization more carefully. - decide CmmRegOff{} = AlwaysInline e - --- Algorithm for unannotated assignments of global registers: --- 1. Delete any sinking assignments that were used by this instruction --- 2. Look for all assignments that reference this register and --- invalidate them. -middleAssignment (Plain n@(CmmAssign reg@(CmmGlobal _) _)) assign - = invalidateUsersOf reg . deleteSinks n $ assign - --- Algorithm for unannotated assignments of *local* registers: do --- nothing (it's a reload, so no state should have changed) -middleAssignment (Plain (CmmAssign (CmmLocal _) _)) assign = assign - --- Algorithm for stores: --- 1. Delete any sinking assignments that were used by this instruction --- 2. Look for all assignments that load from memory locations that --- were clobbered by this store and invalidate them. -middleAssignment (Plain n@(CmmStore lhs rhs)) assign - = let m = deleteSinks n assign - in foldUFM_Directly f m m -- [foldUFM performance] - where f u (xassign -> Just x) m | (lhs, rhs) `clobbers` (u, x) = addToUFM_Directly m u NeverOptimize - f _ _ m = m -{- Also leaky - = mapUFM_Directly p . deleteSinks n $ assign - -- ToDo: There's a missed opportunity here: even if a memory - -- access we're attempting to sink gets clobbered at some - -- location, it's still /better/ to sink it to right before the - -- point where it gets clobbered. How might we do this? - -- Unfortunately, it's too late to change the assignment... - where p r (xassign -> Just x) | (lhs, rhs) `clobbers` (r, x) = NeverOptimize - p _ old = old --} - --- Assumption: Unsafe foreign calls don't clobber memory --- Since foreign calls clobber caller saved registers, we need --- invalidate any assignments that reference those global registers. --- This is kind of expensive. (One way to optimize this might be to --- store extra information about expressions that allow this and other --- checks to be done cheaply.) -middleAssignment (Plain n@(CmmUnsafeForeignCall{})) assign - = deleteCallerSaves (foldRegsDefd (\m r -> addToUFM m r NeverOptimize) (deleteSinks n assign) n) - where deleteCallerSaves m = foldUFM_Directly f m m - f u (xassign -> Just x) m | wrapRecExpf g x False = addToUFM_Directly m u NeverOptimize - f _ _ m = m - g (CmmReg (CmmGlobal r)) _ | callerSaves r = True - g (CmmRegOff (CmmGlobal r) _) _ | callerSaves r = True - g _ b = b - -middleAssignment (Plain (CmmComment {})) assign - = assign - --- Assumptions: --- * Writes using Hp do not overlap with any other memory locations --- (An important invariant being relied on here is that we only ever --- use Hp to allocate values on the heap, which appears to be the --- case given hpReg usage, and that our heap writing code doesn't --- do anything stupid like overlapping writes.) --- * Stack slots do not overlap with any other memory locations --- * Stack slots for different areas do not overlap --- * Stack slots within the same area and different offsets may --- overlap; we need to do a size check (see 'overlaps'). --- * Register slots only overlap with themselves. (But this shouldn't --- happen in practice, because we'll fail to inline a reload across --- the next spill.) --- * Non stack-slot stores always conflict with each other. (This is --- not always the case; we could probably do something special for Hp) -clobbers :: (CmmExpr, CmmExpr) -- (lhs, rhs) of clobbering CmmStore - -> (Unique, CmmExpr) -- (register, expression) that may be clobbered - -> Bool -clobbers (CmmRegOff (CmmGlobal Hp) _, _) (_, _) = False -clobbers (CmmReg (CmmGlobal Hp), _) (_, _) = False --- ToDo: Also catch MachOp case -clobbers (ss@CmmStackSlot{}, CmmReg (CmmLocal r)) (u, CmmLoad (ss'@CmmStackSlot{}) _) - | getUnique r == u, ss == ss' = False -- No-op on the stack slot (XXX: Do we need this special case?) -clobbers (CmmStackSlot (CallArea a) o, rhs) (_, expr) = f expr - where f (CmmLoad (CmmStackSlot (CallArea a') o') t) - = (a, o, widthInBytes (cmmExprWidth rhs)) `overlaps` (a', o', widthInBytes (typeWidth t)) - f (CmmLoad e _) = containsStackSlot e - f (CmmMachOp _ es) = or (map f es) - f _ = False - -- Maybe there's an invariant broken if this actually ever - -- returns True - containsStackSlot (CmmLoad{}) = True -- load of a load, all bets off - containsStackSlot (CmmMachOp _ es) = or (map containsStackSlot es) - containsStackSlot (CmmStackSlot{}) = True - containsStackSlot _ = False -clobbers (CmmStackSlot (RegSlot l) _, _) (_, expr) = f expr - where f (CmmLoad (CmmStackSlot (RegSlot l') _) _) = l == l' - f _ = False -clobbers _ (_, e) = f e - where f (CmmLoad (CmmStackSlot _ _) _) = False - f (CmmLoad{}) = True -- conservative - f (CmmMachOp _ es) = or (map f es) - f _ = False - --- Check for memory overlapping. --- Diagram: --- 4 8 12 --- s -w- o --- [ I32 ] --- [ F64 ] --- s' -w'- o' -type CallSubArea = (AreaId, Int, Int) -- area, offset, width -overlaps :: CallSubArea -> CallSubArea -> Bool -overlaps (a, _, _) (a', _, _) | a /= a' = False -overlaps (_, o, w) (_, o', w') = - let s = o - w - s' = o' - w' - in (s' < o) && (s < o) -- Not LTE, because [ I32 ][ I32 ] is OK - -lastAssignment :: WithRegUsage CmmNode O C -> AssignmentMap -> [(Label, AssignmentMap)] --- Variables are dead across calls, so invalidating all mappings is justified -lastAssignment (Plain (CmmCall _ (Just k) _ _ _)) assign = [(k, mapUFM (const NeverOptimize) assign)] -lastAssignment (Plain (CmmForeignCall {succ=k})) assign = [(k, mapUFM (const NeverOptimize) assign)] -lastAssignment l assign = map (\id -> (id, deleteSinks l assign)) $ successors l - -assignmentTransfer :: FwdTransfer (WithRegUsage CmmNode) AssignmentMap -assignmentTransfer = mkFTransfer3 (flip const) middleAssignment ((mkFactBase assignmentLattice .) . lastAssignment) - -assignmentRewrite :: FwdRewrite FuelUniqSM (WithRegUsage CmmNode) AssignmentMap -assignmentRewrite = mkFRewrite3 first middle last - where - first _ _ = return Nothing - middle :: WithRegUsage CmmNode O O -> AssignmentMap -> GenCmmReplGraph (WithRegUsage CmmNode) O O - middle (Plain m) assign = return $ rewrite assign (precompute assign m) mkMiddle m - middle (AssignLocal l e u) assign = return $ rewriteLocal assign (precompute assign (CmmAssign (CmmLocal l) e)) mkMiddle l e u - last (Plain l) assign = return $ rewrite assign (precompute assign l) mkLast l - -- Tuple is (inline?, reloads) - precompute assign n = foldRegsUsed f (False, []) n -- duplicates are harmless - where f (i, l) r = case lookupUFM assign r of - Just (AlwaysSink e) -> (i, (Plain (CmmAssign (CmmLocal r) e)):l) - Just (AlwaysInline _) -> (True, l) - Just NeverOptimize -> (i, l) - -- This case can show up when we have - -- limited optimization fuel. - Nothing -> (i, l) - rewrite _ (False, []) _ _ = Nothing - -- Note [CmmCall Inline Hack] - -- Conservative hack: don't do any inlining on what will - -- be translated into an OldCmm CmmCalls, since the code - -- produced here tends to be unproblematic and I need to write - -- lint passes to ensure that we don't put anything in the - -- arguments that could be construed as a global register by - -- some later translation pass. (For example, slots will turn - -- into dereferences of Sp). See [Register parameter passing]. - -- ToDo: Fix this up to only bug out if all inlines were for - -- CmmExprs with global registers (we can't use the - -- straightforward mapExpDeep call, in this case.) ToDo: We miss - -- an opportunity here, where all possible inlinings should - -- instead be sunk. - rewrite _ (True, []) _ n | not (inlinable n) = Nothing -- see [CmmCall Inline Hack] - rewrite assign (i, xs) mk n = Just $ mkMiddles xs <*> mk (Plain (inline i assign n)) - - rewriteLocal _ (False, []) _ _ _ _ = Nothing - rewriteLocal assign (i, xs) mk l e u = Just $ mkMiddles xs <*> mk n' - where n' = AssignLocal l e' u - e' = if i then wrapRecExp (inlineExp assign) e else e - -- inlinable check omitted, since we can always inline into - -- assignments. - - inline :: Bool -> AssignmentMap -> CmmNode e x -> CmmNode e x - inline False _ n = n - inline True _ n | not (inlinable n) = n -- see [CmmCall Inline Hack] - inline True assign n = mapExpDeep (inlineExp assign) n - - inlineExp assign old@(CmmReg (CmmLocal r)) - = case lookupUFM assign r of - Just (AlwaysInline x) -> x - _ -> old - inlineExp assign old@(CmmRegOff (CmmLocal r) i) - = case lookupUFM assign r of - Just (AlwaysInline x) -> - case x of - (CmmRegOff r' i') -> CmmRegOff r' (i + i') - _ -> CmmMachOp (MO_Add rep) [x, CmmLit (CmmInt (fromIntegral i) rep)] - where rep = typeWidth (localRegType r) - _ -> old - inlineExp _ old = old - - inlinable :: CmmNode e x -> Bool - inlinable (CmmCall{}) = False - inlinable (CmmForeignCall{}) = False - inlinable (CmmUnsafeForeignCall{}) = False - inlinable _ = True - -rewriteAssignments :: CmmGraph -> FuelUniqSM CmmGraph -rewriteAssignments g = do - g' <- annotateUsage g - g'' <- liftM fst $ dataflowPassFwd g' [(g_entry g, fact_bot assignmentLattice)] $ - analRewFwd assignmentLattice assignmentTransfer assignmentRewrite - return (modifyGraph eraseRegUsage g'') - --------------------- -- prettyprinting @@ -671,8 +218,6 @@ instance Outputable DualLive where if isEmptyUniqSet stack then PP.empty else (ppr_regs "live on stack =" stack)] --- ToDo: Outputable instance for UsageMap and AssignmentMap - my_trace :: String -> SDoc -> a -> a my_trace = if False then pprTrace else \_ _ a -> a